1. Field of the Invention
This invention relates to a camera provided with an eyepiece, and in particular, to a camera having a picture plane of size as small as nearly half of a 135-format film or a silver halide 35-nm film.
2. Description of Related Art
In a camera having a picture plane of small size, when a conventional eyepiece is used as it is, an observation image becomes small and an photographer suffers from undue fatigue in using the camera.
Thus, in order to enable a large image to be observed through a finder, it is necessary to reduce the focal length of the eyepiece and to increase a finder magnification.
Conventional examples in which the focal length of the eyepiece is reduced are disclosed in Japanese Patent Publication Nos. Sho 57-60612 and Hei 7-107581 and Japanese Patent Kokai No. Hei 11-337847.
In order to render a finder easy to see, there is the need to ensure a distance from the eyepiece to the pupil position of an observer as long as possible and to minimize vignetting. In this case also, it becomes necessary to sufficiently increase a distance from an observation plane to a first lens component of the eyepiece.
An eyepiece in which the distance from the observation plane to the entrance surface of the first lens component thereof is longer than the focal length is set forth, for example, in Japanese Patent No. 2726261 in addition to Publication No. Hei 7-107581 mentioned above.
The present invention provides a single-lens reflex camera which comprises a screen on which an image of an object is projected, a plurality of reflection surfaces for erecting the image on the screen, and an eyepiece system with positive refracting power for observing the image. In this case, the eyepiece system includes, in order from the object side, a first lens component with positive refracting power, a second lens component with positive refracting power, and a third lens component with negative refracting power so that spacings between the first lens component and the second lens component and between the second lens component and the third lens component are changed to thereby make a diopter adjustment, and the single-lens reflex camera satisfies the following conditions:
0.15 less than tan(S) less than 0.35xe2x80x83xe2x80x83(1)
2.00 less than fb/Y less than 4.00xe2x80x83xe2x80x83(2)
xe2x88x920.80 less than f3/f less than xe2x88x920.40xe2x80x83xe2x80x83(3)
where S is an angle, at a diopter of 0 mxe2x88x921, made by the most off-axis chief ray passing through a point on the optical axis at a distance of 23 mm along the optical axis from the exit surface of the third lens component with the optical axis; fb is an air-equivalent length, at a diopter of 0 mxe2x88x921, from the screen to the entrance surface of the first lens component; Y is a diagonal length of the picture plane on the screen; f3 is the focal length of the third lens component; and f is the focal length, at a diopter of 0 mxe2x88x921, of the entire system from the screen to the exit surface of the eyepiece system.
Further, the present invention provides a camera which comprises a screen on which an image of an object is projected, a plurality of reflection surfaces for erecting the image on the screen, and an eyepiece system with positive refracting power for observing the image. In this case, the eyepiece system includes, in order from the object side, a first lens component with positive refracting power, a second lens component with positive refracting power, and a third lens component with negative refracting power so that spacings between the first lens component and the second lens component and between the second lens component and the third lens component are changed to thereby make a diopter adjustment, and the camera satisfies Condition (1) and the following condition:
xe2x88x920.65 less than f3/f less than xe2x88x920.45xe2x80x83xe2x80x83(4)
Still further, the present invention provides a camera which comprises a screen on which an image of an object is projected, a plurality of reflection surfaces for erecting the image on the screen, and an eyepiece system with positive refracting power for observing the image. In this case, the eyepiece system includes, in order from the object side, a first lens component with positive refracting power, a second lens component with positive refracting power, and a third lens component with negative refracting power so that spacings between the first lens component and the second lens component and between the second lens component and the third lens component are changed to thereby make a diopter adjustment, and the camera satisfies Condition (1) and the following condition:
15 mm less than Y less than 30 mmxe2x80x83xe2x80x83(5)
The present invention provides a camera which comprises a screen on which an image of an object is projected, a plurality of reflection surfaces for erecting the image on the screen, and an eyepiece system with positive refracting power for observing the image. In this case, the eyepiece system includes, in order from the object side, a first lens component with positive refracting power, a second lens component with positive refracting power, and a third lens component with negative refracting power so that spacings between the first lens component and the second lens component and between the second lens component and the third lens component are changed to thereby make a diopter adjustment, and the camera satisfies Condition (1) and the following conditions:
2.70 less than fb/Y less than 3.20xe2x80x83xe2x80x83(6)
xe2x80x83xe2x88x920.80 less than f3/f less than xe2x88x920.30xe2x80x83xe2x80x83(7)
According to the present invention, preferably, each of the first lens component, the second lens component, and the third lens component is constructed with a single lens or a cemented lens.
According to the present invention, preferably, only the second lens component is moved to thereby make a diopter adjustment.
The present invention provides a camera which comprises a screen on which an image of an object is projected, a plurality of reflection surfaces for erecting the image on the screen, and an eyepiece system with positive refracting power for observing the image. In this case, the eyepiece system includes, in order from the object side, a first lens component with positive refracting power, a second lens component with positive refracting power, and a third lens component with negative refracting power, and the camera satisfies the following conditions:
2.5 less than fbxe2x80x2/Y less than 4.0xe2x80x83xe2x80x83(8)
xe2x88x921.0 less than f3/fxe2x80x2 less than xe2x88x920.2xe2x80x83xe2x80x83(9)
0.4 less than f1/fxe2x80x2 less than 0.95xe2x80x83xe2x80x83(10)
where fbxe2x80x2 is an air-equivalent length, at a diopter of xe2x88x920.5 (mxe2x88x921), from the screen to the entrance surface of the first lens component; fxe2x80x2 is the focal length of the entire system from the screen to the exit surface of the eyepiece system at a diopter of xe2x88x920.5 (mxe2x88x921); and f1 is the focal length of the first lens component.
The present invention provides a camera which comprises a screen on which an image of an object is projected, a plurality of reflection surfaces for erecting the image on the screen, and an eyepiece system with positive refracting power for observing the image. In this case, the eyepiece system includes, in order from the object side, a first lens component with positive refracting power, a second lens component with positive refracting power comprised of a single meniscus lens element with a convex surface directed toward the object side, and a third lens component with negative refracting power as a whole in which the refracting power of a pupil-side surface is stronger than that of an object-side surface, and the camera satisfies Conditions (8), (9), and (10).
In the present invention, instead of the screen on which the image of the object is projected, the camera may be provided with an electronic viewfinder which includes a liquid crystal display element having an image plane for displaying the image of the object.
Alternatively, in the present invention, instead of the screen on which the image of the object is projected, the camera may be provided with a finder which includes an objective optical system forming the image plane of the object.
In these cases, Y becomes Yxe2x80x2 (a diagonal length of a picture plane on the image plane), fb becomes fxe2x80x2b (an air-equivalent length from the image plane to the entrance surface of the first lens component at a diopter of 0 (mxe2x88x921)), fbxe2x80x2 becomes fxe2x80x2bxe2x80x2 (an air-equivalent length from the image plane to the entrance surface of the first lens component at a diopter of xe2x88x920.5 (mxe2x88x921)), f becomes fxe2x80x3 (the focal length, at a diopter of 0 (mxe2x88x921), of the entire system from the image plane to the exit surface of the eyepiece system), and fxe2x80x2 becomes fxe2x80x2xe2x80x3 (the focal length, at a diopter of xe2x88x920.5 (mxe2x88x921), of the entire system from the image plane to the exit surface of the eyepiece system).
These and other features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.